Method for reducing haze in a fire resistant polycarbonate composition

ABSTRACT

A method to reduce haze in the production of fire resistant polycarbonate compositions comprising flame retardant salts, wherein the salt is blended with a first polycarbonate to form a concentrate, and the concentrate is then added to a second polycarbonate resin.

BACKGROUND OF THE INVENTION

[0001] This invention relates to methods of producing transparent, fireresistant polycarbonate compositions and more particularly transparent,fire resistant polycarbonate compositions comprising flame retardantsalts.

[0002] Plastics, and in particular polycarbonates, are increasinglybeing used to replace metals in a wide variety of applications, from carexteriors to aircraft interiors. The use of polycarbonate instead ofmetal decreases weight, improves sound dampening, and makes assembly ofthe device easier. Unfortunately, polycarbonates are inherentlyflammable, and thus require the addition of flame retardants. A varietyof different materials have been used, some of which are set forth inU.S. Pat. Nos. 3,971, 4,028,297, 4,110,299, 4,130,530, 4,303,575,4,335,038, 4,552,911, 4,916,194, 5,218,027, and 5,508,323. The challengeis to identify economical, environmentally friendly flame retardantadditives that provide the requisite flame resistance, but withoutcompromising desirable polycarbonate properties such as strength andclarity.

[0003] Flame resistance in polycarbonate compositions may be achievedusing a sulfonic acid salt such as potassium perfluorobutane sulfonate(also known as “Rimar salt”, or “KPFBS”) as disclosed, for example, inU.S. Pat. No. 3,775,367. While flame resistant, transparentpolycarbonate compositions may be produced using KPFBS, optimum flameresistance is found for levels of salt that can result in haze,especially for thicker samples. The amount of flame retardant that canbe added when an optically clear product is desired is thus limited.Addition of synergistic additives such as tetrabromobisphenol A toimprove flame retardancy is not possible where “ECO-friendly” standardthat prohibit the inclusion of bromine or chlorine are in place.Accordingly, there remains a need in the art for methods of producingpolycarbonates that are not only highly flame resistant, but alsotransparent.

BRIEF SUMMARY OF THE INVENTION

[0004] The above discussed and other drawbacks and deficiencies of theprior art are overcome or alleviated by a method for reducing haze infire resistant polycarbonate compositions, comprising

[0005] blending a flame retardant salt with a first polycarbonate toproduce a concentrate; and,

[0006] blending the concentrate with a second polycarbonate to form atransparent, fire resistant polycarbonate composition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] It has surprisingly been found that highly flame resistant andtransparent polycarbonate compositions may be obtained by blending aflame retardant salt with a first polycarbonate to produce aconcentrate, then blending the concentrate with a second polycarbonateto form a transparent, fire resistant polycarbonate composition. Theconcentrate is preferably a pelletized blend of KPFBS and polycarbonate.In another preferred embodiment, the first polycarbonate and the secondpolycarbonate are the same.

[0008] Not wishing to be bound by any theory, it is believed that thepresent method of using the flame retardant salt-polycarbonateconcentrate aids in completely dissolving the salt into the finalpolycarbonate composition by giving the salt crystals an additional heathistory. The additional heat history may allow for effectivelysolubilizing greater amounts of salt into the matrix. The present methodallows for the use of higher levels of flame retardant salt, therebyproviding robust flame performance while at the same time maintainingpolymer transparency.

[0009] Non-limiting examples of suitable sulfonic acid salts areperfluoroalkane sulfonate alkali metal, C₁-C₆ alkylammonium, or ammoniumsalts. Such salts are described in the above-mentioned U.S. Pat. No.3,775,367, and include, for example, salts such as sodium, potassium, ortetraethyl ammonium perfluoromethylbutane sulphonate; sodium, potassium,or tetraethyl ammonium perfluoromethane sulphonate; sodium, potassium,or tetraethyl ammonium perfluoroethane sulphonate; sodium, potassium, ortetraethyl ammonium perfluoropropane sulphonate; sodium, potassium, ortetraethyl ammonium perfluorohexane sulphonate; sodium, potassium, ortetraethyl ammonium perfluoroheptane sulphonate; sodium, potassium, ortetraethyl ammonium perfluoroctanesulphonate; sodium, potassium, ortetraethyl ammonium perfluorobutane sulfonate; and sodium, potassium, ortetraethyl ammonium diphenylsulfon-3-sulphonate; and mixtures comprisingat least one of the foregoing salts. Potassium perfluorobutane sulfonate(KPFBS) and potassium diphenylsulfon-3-sulphonate (KSS) are particularlypreferred.

[0010] The salt, and KPFBS in particular, is present in the finalcomposition in quantities effective to achieve a flame resistance ratingof UL94-VO at 3.2 millimeters. Generally, effective amounts of flameretardant salt present in the final composition is about 0.01 to about1.0, preferably about 0.05 to about 0.20, and most preferably about 0.06to about 0.12, and even more preferably 0.08-0.10% by weight based uponthe total weight of the resin in the final composition. To achieve thesefinal concentrations, it is convenient to produce a concentrate whereinthe amount of flame retardant salt in the concentrate is about 0.1 toabout 5.0, preferably about 0.5 to about 2.0, and most preferably about0.8 to about 1.2% by weight of the total amount of the concentrate.

[0011] The polycarbonate component may be made by interfacial processesor by catalytic transesterification, may be either branched or linear instructure, and may include functional substituents. As used herein, theterms “polycarbonate” and “polycarbonate composition” includescompositions having structural units of the formula (I):

[0012] in which at least about 60 percent of the total number of R¹groups are aromatic organic radicals and the balance thereof arealiphatic, alicyclic, or aromatic radicals. Preferably, R¹ is anaromatic organic radical and, more preferably, a radical of the formula(II):

—A ¹ —Y ¹ —A ²—  (II)

[0013] wherein each of A¹ and A² is a monocyclic divalent aryl radicaland Y¹ is a bridging radical having one or two atoms which separate A¹from A². In an exemplary embodiment, one atom separates A¹ from A².Illustrative non-limiting examples of radicals of this type are —O—,—S—, —S(O)—, —S(O)₂—, —C(O)—, methylene, cyclohexyl-methylene,2-[2.2.1]-bicycloheptylidene, ethylidene, isopropylidene,neopentylidene, cyclohexylidene, cyclopentadecylidene,cyclododecylidene, and adamantylidene. The bridging radical Y¹ can be ahydrocarbon group or a saturated hydrocarbon group such as methylene,cyclohexylidene or isopropylidene.

[0014] Polycarbonates can be produced by the interfacial reaction ofdihydroxy compounds in which only one or two atoms separate A¹ and A².As used herein, the term “dihydroxy compound” includes, for example,bisphenol compounds having general formula (III) as follows:

[0015] wherein R^(a) and R^(b) each represent a monovalent hydrocarbongroup and may be the same or different; p and q are each independentlyintegers from 0 to 4; and X^(a) represents one of the groups of formula(IV):

[0016] wherein R^(c) and R^(d) each independently represent a hydrogenatom or a monovalent linear or cyclic hydrocarbon group and Re is adivalent hydrocarbon group.

[0017] Some illustrative, non-limiting examples of suitable dihydroxycompounds include the dihydroxy-substituted aromatic hydrocarbonsdisclosed by name or formula (generic or specific) in U.S. Pat. No.4,217,438, which is incorporated herein by reference. A nonexclusivelist of specific examples of the types of bisphenol compounds that maybe represented by formula (III) includes the following:

[0018] 1,1-bis(4-hydroxyphenyl) methane;

[0019] 1,1-bis(4-hydroxyphenyl) ethane;

[0020] 2,2-bis(4-hydroxyphenyl) propane (hereinafter “bisphenol A” or“BPA”);

[0021] 2,2-bis(4-hydroxyphenyl) butane;

[0022] 2,2-bis(4-hydroxyphenyl) octane;

[0023] 1,1-bis(4-hydroxyphenyl) propane;

[0024] 1,1-bis(4-hydroxyphenyl) n-butane;

[0025] bis(4-hydroxyphenyl) phenylmethane;

[0026] 2,2-bis(4-hydroxy-1-methylphenyl) propane;

[0027] 1,1-bis(4-hydroxy-t-butylphenyl) propane;

[0028] 2,2-bis(4-hydroxy-phenyl) propane;

[0029] 1,1-bis(4-hydroxyphenyl) cyclopentane; and

[0030] 1,1-bis(4-hydroxyphenyl) cyclohexane.

[0031] It is also possible to employ two or more different dihydricphenols or a copolymer of a dihydric phenol with a glycol or with ahydroxy- or acid-terminated polyester or with a dibasic acid or hydroxyacid in the event a carbonate copolymer rather than a homopolymer isdesired for use. Polyarylates and polyester-carbonate resins or theirblends can also be employed. Branched polycarbonates are also useful, aswell as blends of linear polycarbonate and a branched polycarbonate. Thebranched polycarbonates may be prepared by adding a branching agentduring polymerization.

[0032] These branching agents are well known and may comprisepolyfunctional organic compounds containing at least three functionalgroups, which may be hydroxyl, carboxyl, carboxylic anhydride, andmixtures thereof. Specific examples include trimellitic acid,trimellitic anhydride, trimellitic trichloride, tris-p-hydroxy phenylethane, isatin-bis-phenol, tris-phenol TC(1,3,5-tris((p-hydroxyphenyl)isopropyl)benzene), tris-phenol PA(4(4(1,1-bis(p-hydroxyphenyl)-ethyl) alpha, alpha-dimethylbenzyl)phenol, trimesic acid and benzophenone tetracarboxylic acid. Thebranching agents may be added at a level of about 0.05-2.0 weightpercent. Branching agents and procedures for making branchedpolycarbonates are described in U.S. Pat. Nos. 3,635,895 and 4,001,184,which are incorporated by reference. All types of polycarbonate endgroups are contemplated as being within the scope of the presentinvention.

[0033] Preferred polycarbonates are based on bisphenol A, in which eachof A¹ and A² is p-phenylene and Y¹ is isopropylidene. Preferably, theaverage molecular weight of the polycarbonate is in the range of about5,000 to about 100,000, more preferably in the range of about 10,000 toabout 65,000, and most preferably in the range of about 15,000 to about35,000. Furthermore the polycarbonate has a melt viscosity rate (MVR) ofabout 4 to about 30 cm³/10 min.

[0034] Additionally, the polycarbonate composition may include variousadditives ordinarily incorporated in resin compositions of this type.Such additives are, for example, fillers or reinforcing agents; heatstabilizers; antioxidants; light stabilizers; plasticizers; antistaticagents; mold releasing agents; additional resins; and blowing agents.Examples of fillers or reinforcing agents include glass fibers,asbestos, carbon fibers, silica, talc, and calcium carbonate. Examplesof heat stabilizers include triphenyl phosphite,tris-(2,6-dimethylphenyl)phosphite, tris-(mixed mono-anddi-nonylphenyl)phosphite, dimethylbenzene phosphonate,tris-(2,4-di-t-butylphenyl)phosphite, and trimethyl phosphate. Examplesof antioxidants includeoctadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, andpentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].Examples of light stabilizers include2-(2-hydroxy-5-methylphenyl)benzotriazole,2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole and 2-hydroxy-4-n-octoxybenzophenone. Examples of plasticizers includedioctyl-4,5-epoxy-hexahydrophthalate,tris-(octoxycarbonylethyl)isocyanurate, tristearin and epoxidizedsoybean oil. Examples of the antistatic agent include glycerolmonostearate, sodium stearyl sulfonate, and sodiumdodecylbenzenesulfonate. Examples of mold releasing agents includestearyl stearate, pentaerythritol tetrastearate, beeswax, montan wax andparaffin wax. Examples of other resins include but are not limited topolypropylene, polystyrene, polymethyl methacrylate, and polyphenyleneoxide. Combinations of any of the foregoing additives may be used. Suchadditives may be mixed at a suitable time during the mixing of thecomponents for forming the composition. A preferred time is during theblending of the concentrate and the second polycarbonate.

[0035] In particular, other flame retarding components may be present inthe compositions, for example cyclic siloxanes, at levels effective toimpart improved fire-resistance properties. Suitable quantities willgenerally be in the range of about 0.01 to about 0.5 parts per hundredparts by weight of resin (phr), preferably about 0.02 to about 0.30 phr.Suitable cyclic siloxanes, which may be present, include those havingthe general formula (V)

[0036] wherein n is 0-7 and each R is independently an alkyl grouphaving from 1 to about 36 carbons, an alkoxy group having from 1 toabout 36 carbons, a fluorinated or perfluorinated alkyl or alkoxy grouphaving from 1 to about 36 carbons, an arylalkoxy group having from 7 toabOut 36 carbons, an aryl group having from 6 to about 14 carbons, anaryloxy group having from 6 to about 14 carbons, a fluorinated orperfluorinated aryl group having from 6 to about 14 carbons, and analkylaryl group having from 7 to about 36 carbons. Specific examples ofcyclic siloxanes include but are not limited tooctaphenylcyclotetrasiloxane, hexameethylcyclotrisiloxane,octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane,dodecamethylcyclohexasiloxane, trimethyltriphenylcyclotrisiloxane, andtetramethyltetraphenylcyclotetrasiloxane.

[0037] In the practice of the process, the flame retardant salt isblended with a first polycarbonate to form a concentrate that is anintimate blend. The concentrate is further blended with a secondpolycarbonate to produce a final intimate blend. Such conditionsresulting in an intimate blend often include mixing in single ortwin-screw type extruders or similar mixing devices well known in theart, which can apply shear to the components. It is often advantageousto apply a vacuum to the melt through at least one or more vent ports inthe extruder to remove volatile impurities in the composition.

[0038] In a preferred embodiment, the concentrate is pelletized. Thefirst polycarbonate and flame retardant salt blend is pumped in moltenform through a strand die to a water bath and pelletizer. The pelletizedconcentrate is then further blended with a second polycarbonate.

[0039] Those of ordinary skill in the art will be able to adjustblending times and temperatures, as well as component addition, withoutundue additional experimentation.

[0040] The invention is further illustrated by the followingnon-limiting Examples.

EXAMPLES

[0041] The following examples were prepared according to theformulations listed in Tables 1 and 2. All amounts are weight percentbased on the total resin weight unless otherwise indicated.

[0042] Laboratory scale comparative examples (e.g., Example 1, Table 1)were made by powder blending the components in the amounts indicated inTable 1, followed by feeding the blend to a twin screw extruder operatedat 300° C. and about 20 kg/hr. The extruded strands were cut intopellets and the pellets were injection molded at 285 to 300° C. intoappropriate test samples for the testing.

[0043] The masterbatch comprising KPFBS in accordance with the presentinvention was prepared using the same procedure, except that theformulation comprised 99% of the lower molecular weight polycarbonateresin and 1% of the KPFBS. Laboratory scale examples (e.g., Example 2,Table 1) in accordance with the present invention were also preparedusing the same procedure, except that as indicated, the KPFBS of thecomparative examples was replaced in the blend fed to the extruder withthe pelletized master batch of KPFBS containing the equivalent quantityof KPFBS as in the comparative example.

[0044] Melt volume ratio (MVR) of the examples was measured on 1.2kilogram at 300° C. in accordance with ASTM D1238.

[0045] After conditioning samples for 2 days at 23° C., 50% relativehumidity, flammability tests on 3.2 mm thick samples were performedfollowing the procedure of Underwriter's Laboratory Bulletin 94 entitled“Tests for Flammability of Plastic Materials, UL94”. Four sets of fivesamples for each formulation were tested. According to UL 94, thematerials were classified as UL94 V-0, UL94 V-1, or UL94 V-2.

[0046] Yellowness Index (YI) for laboratory scale samples was measuredin accordance with ASTM D1925. Transparency is described by twoparameters, percent transmission and percent haze. Percent transmissionand percent haze for laboratory scale samples were determined using ASTMD1003. TABLE 1 Component Example 1* Example 2 Polycarbonate resin, MW21,800 64.35 54.45 Polycarbonate resin, MW 30,500 35 35Octaphenyltetrasiloxane 0.1 0.1 Pentaerythritol stearate 0.35 0.35 KPFBS0.1 — Phosphite stabilizer 0.1 0.1 Concentrate (1 wt. % KPFBS) — 10Properties MVR 15.1 15.2 % Transmittance (2.5 mm) 90.5 90.7 YI (2.5 mm)1.6 1.5 Haze 1 0.9 % Transmittance (3.2 mm) 90.2 90.5 YI (3.2 mm) 1.91.7 Haze (3.2 mm) 1.6 0.7 UL-94 (3.2 mm) V-0 V-0

[0047] Haze is often exacerbated for thicker samples. As can be seen byreference to the above data, haze for samples at 3.2 mm show significantimprovement over the control.

[0048] In addition to the haze reduction, the thicker section runnersfrom the moldings were observed to exhibit bubbles, with the inventionexample exhibiting the least bubbles. On a scale of 1 (no bubbles) to 10(runner completely covered with bubbles) the example of the inventionhad a rating of 1 and the comparative example had a rating of 7.

[0049] Manufacturing scale examples (e.g., Comparative example 3, Table2) were prepared by making a uniform powder blend of 80 kg of the lowermolecular weight polycarbonate resin with the quantities of KPFBS,octaphenyltetrasiloxane, pentaerythritol tetrastearate, phosphitestabilizer, and pigments listed in Table 2. The blend was fed to a 75 mmtwin-screw extruder at a 4.7% ratio simultaneously with 100% of thelower MW polycarbonate resin of Table 2 at 44.6% ratio and 100% of thehigher MW polycarbonate resin of Table 2 at 50.7% ratio to yield anoverall batch size of 2000 kg of the formulation of Table 2. The blendwas extruded at a temperature setting from 200° C. to 280° C. intostrands and the strands cut into pellets. The pellets were subsequentlyinjection molded at 302 to 307° C. into plaques 4.5 mm in thickness.

[0050] The Master batch of KPFBS was prepared essentially in the samemanner as described above for Comparative example 3, except that theuniform powder blend consisted of 11.0 Kg of KPFBS and 85 kg of thelower MW polycarbonate resin, which was fed to the extruder at a ratioof 8.7% simultaneously with 100% of the lower MW polycarbonate resin ata 91.3% ratio to yield an overall batch size of 1101 kg.

[0051] Manufacturing scale examples in accordance with the presentinvention (e.g., Example 4 of Table 2) were prepared by making a uniformpowder blend of 78 kg of the lower molecular weight polycarbonate resinof Table 2 with the quantities of octaphenyltetrasiloxane,pentaerythritol tetrastearate, phosphite stabilizer and pigment andstabilizers listed in Table 2. The blend was fed to a 75 mm twin screwextruder at a 7.14% ratio simultaneously with the KPFBS master batchpellets at a 7.94% ratio, 100% of the lower MW polycarbonate resin at44.68% ratio and 100% of the higher MW polycarbonate resin at a 40.24%ratio to yield an overall batch size of 1200 kg of the formulation ofTable 2. The blend was extruded at temperature setting from 200° C. to280° C. into strands and the strands cut into pellets. The pellets weresubsequently injection molded at 302 to 307° C. into plaques 4.5 mm inthickness.

[0052] Haze measurements for manufacturing scale samples were performedon a Macbeth Spectrophotometer, Model COLOR-EYE 7000, manufactured byMacbeth, a division of Kollmorgen Instruments Corp., New York. Beforethe actual measurement, the spectrophotometer was calibrated by using anultraviolet filter to filter the 340-400 nm spectral region, and thenplacing the ZERO calibration standard followed by the WHITE calibrationstandard (ceramic) in the viewport. After calibration, haze measurementswere performed on 4.5 mm thick chips by placing the samples in theviewport. Three chips of each sample were made and haze measurementswere done twice on each of the three chips of a particular sample. Thefinal output provides a percent haze number relative to the ZERO and theWHITE calibration standards. TABLE 2 Example 3* Example 4 Component Kg %Kg % Polycarbonate resin, MW 971.7 48.6 536.2 44.7 21,800 Polycarbonateresin, MW 1015 50.75 560.9 46.7 30,500 Octaphenyltetrasiloxane 2.0 0.11.19 0.1 Pentaerythritol stearate 6.94 0.347 4.17 0.347 KPFBS 1.6 0.08 —— Phosphite stabilizer 1.8 0.09 1.07 0.09 Concentrate (1 wt. % KPFBS) —— 95.3 7.94

[0053] Percent haze in 12 pelletized samples prepared by the method ofcomparative example 3 was found to be in the range from 1.58 to 4.59,average of 3.13, with a standard deviation of 0.87. Percent haze for 9samples formed by the method of Example 4 was found to be in the rangefrom 0.51 to 1.23, average of 0.71, with a standard deviation of 0.23

[0054] While preferred embodiments have been shown and described,various modifications and substitutions may be made thereto withoutdeparting from the spirit and scope of the invention. Accordingly, it isto be understood that the present invention has been described by way ofillustration and not limitation.

What is claimed is:
 1. A method for reducing haze in fire resistantpolycarbonate compositions, comprising: blending flame retardant saltwith a first polycarbonate to produce a concentrate; pelletizing theconcentrate; and, blending the pelletized concentrate with a secondpolycarbonate to form a fire resistant polycarbonate composition.
 2. Themethod of claim 1, wherein the flame retardant salt is a perfluoroalkanealkali metal, C₁-C₆ alkylammonium, or ammonium sulphonate.
 3. The methodof claim 1, wherein the flame retardant salt is sodium, potassium, ortetraethyl ammonium perfluoromethylbutane sulphonate; sodium, potassium,or tetraethyl ammonium perfluoromethane sulphonate; sodium, potassium,or tetraethyl ammonium perfluoroethane sulphonate; sodium, potassium, ortetraethyl ammonium perfluoropropane sulphonate; sodium, potassium, ortetraethyl ammonium perfluorohexane sulphonate; sodium, potassium, ortetraethyl ammonium perfluoroheptane sulphonate; sodium, potassium, ortetraethyl ammonium perfluoroctanesulphonate; sodium, potassium, ortetraethyl ammonium perfluorobutane sulfonate; and sodium, potassium, ortetraethyl ammonium diphenylsulfon-3-sulphonate; and mixtures comprisingat least one of the foregoing salts.
 4. The method of claim 1, whereinthe flame retardant salts is potassium perfluorobutane sulfonate,potassium diphenylsulfon-3-sulphonate, or a mixture comprising at leastone of the foregoing salts.
 5. The method of claim 1, wherein the flameretardant salt is potassium perfluorobutane sulfonate.
 6. The method ofclaim 1, wherein the flame retardant salt is present in the concentratein an amount from about 0.10 to about 5.0 weight percent based upon thetotal weight of the concentrate.
 7. The method of claim 1, wherein thefirst polycarbonate is the same as the second polycarbonate.
 8. Themethod of claim 1, wherein the flame retardant salt is present in thefire resistant polycarbonate composition in amounts of about 0.01 toabout 1.0 weight percent based upon the total weight of thepolycarbonate.
 9. The method of claim 1, wherein the flame retardantsalt is present in the fire resistant polycarbonate composition inamounts of about 0.05 to about 0.20 weight percent based upon the totalweight of the polycarbonate.
 10. The method of claim 1, wherein theflame retardant salt is present in the fire resistant polycarbonatecomposition in amounts of about 0.06 to about 0.12 weight percent basedupon the total weight of the polycarbonate.
 11. The method of claim 1,wherein the flame retardant salt is present in the fire resistantpolycarbonate composition in amounts of about 0.08 to about 0.10 weightpercent based upon the total weight of the polycarbonate.
 12. The methodof claim 1, further comprising blending with the concentrate and secondpolycarbonate a filler, reinforcing agent, heat stabilizer, antioxidant,light stabilizer, plasticizer, antistatic agent, mold releasing agent,additional resin, blowing agent or combinations comprising at least oneof the foregoing.
 13. The method of claim 1, wherein the compositionfurther comprises a cyclic siloxane.
 14. The method of claim 13, whereinthe cyclic siloxane is present in the flame resistant polycarbonatecomposition in an amount from about 0.01 to about 0.5 parts per hundredparts by weight of the total resin.
 15. The method of claim 13, whereinthe cyclic siloxane has the general formula (V)

wherein n is 0-7 and each R is independently an alkyl group having from1 to about 36 carbons, an alkoxy group having from 1 to about 36carbons, a fluorinated or perfluorinated alkyl or alkoxy group havingfrom 1 to about 36 carbons, an arylalkoxy group having from 7 to about36 carbons, an aryl group having from 6 to about 14 carbons, an aryloxygroup having from 6 to about 14 carbons, a fluorinated or perfluorinatedaryl group having from 6 to about 14 carbons, or an alkylaryl grouphaving from 7 to about 36 carbons.
 16. The method of claim 13, whereinthe cyclic siloxane is octaphenylcyclotetrasiloxane,hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,trimethyltriphenylcyclotrisiloxane, andtetramethyltetraphenylcyclotetrasiloxane.
 17. The method of claim 13,wherein the cyclic siloxane is octaphenylcyclotetrasiloxane.